The present invention relates to a ball roller rolling member which is utilized as rolling member for a rolling bearing or rolling motion guide device.
The inventor of the subject application had already obtain the U.S. patent (U.S. Pat. No. 6,398,417) relating to a ball roller rolling member which has a combined characteristics of self-aligning property of a ball and high rigidity of a roller.
The term “ball roller” used herein means a member which has a large load (carrying) capacity substantially equivalent to that of the roller as well as easily handling characteristic as a ball, and the ball roller rolling member generally comprises a rolling curved portion and end spherical portions disposed on both sides of the rolling curved portion. The end spherical portions are positioned on one virtual spherical surface, and the rolling curved portion has a sectional circular-arc shape having a radius of curvature larger than that of the end spherical portion.
However, in the ball roller rolling member disclosed in the U.S. Pat. No. 6,398,417, a distance between the end spherical portions is longer than the maximum diameter of the rolling curved portion, so that this ball roller rolling member can not be used for a rotating bearing or linear motion guide having a crossing arrangement in which rotational axes of the rolling members are perpendicular alternately to each other between a pair of track grooves provided with perpendicular track surfaces of the rotting bearing or linear motion guide.
Moreover, both the rolling curved portion and the end spherical portions have the spherical surfaces, and when this ball roller rolling member is freely rolled, it rolls in various direction unevenly as like a ball, and therefore, it is difficult to automatically align the ball roller rolling members by a parts-feeder and to separate defective products.
Furthermore, in a case where the ball roller is precisely ground, by using a lapping machine, the ball roller rolling member is generally put into spiral grooves formed to upper and lower discs from the central portion thereof, and the discs are relatively rotated so as to grind the contact surface thereof while rolling the ball roller rolling member so that the spiral grooves is directed from the central portion towards the outer side portion. At this time, there causes a peripheral speed difference between the outer edge and the inner edge of the spiral groove, and according to such peripheral speed difference, grinding amount on the outer edge portion is made larger than that on the inner edge portion, so that the ball roller rolling member, which has been once ground, is again set to the lapping machine in a state reverse in position to the above state and is then ground to thereby grind it substantially laterally uniformly.
However, since a conventional ball roller rolling member is generally laterally symmetrical, it is difficult to discriminate the lateral portions of the once ground ball roller member, that is, which is the ground lateral one side, i.e., inner circular side of the spiral groove, and it is hence difficult to precisely grind the ball roller rolling member by using the lapping machine.
The inventors also proposed a method of simultaneously grinding rolling surfaces of ball roller rolling members, which are magnetically adsorbed so as to form a row of raw material balls in form of rod, by a center-less grinding as disclosed in Japanese Laid-open Patent Publication No. 2002-178244.
However, in such prior art technology, since the raw material balls contact each other in point-contact state, there was a fear of displacing or shifting the contacting portion at the time of grinding the ball roller rolling member, which may lead to worse working performance to the rolling surfaces of the balls.